On the Eddington limit for relativistic accretion discs

Abstract

Standard accretion disc model relies upon several assumptions, the most important of which is geometrical thinness. Whenever this condition is violated, new physical effects become important such as radial energy advection and mass loss from the disc. These effects are important, for instance, for large mass accretion rates when the disc approaches its local Eddington limit. In this work, we study the upper limits for standard accretion disc approximation and find the corrections to the standard model that should be considered in any model aiming on reproducing the transition to super-Eddington accretion regime. First, we find that for thin accretion disc, taking into account relativistic corrections allows to increase the local Eddington limit by about a factor of two due to stronger gravity in General Relativity (GR). However, violation of the local Eddington limit also means large disc thickness. To consider consequently the disc thickness effects, one should make assumptions upon the twodimensional rotation law of the disc. For rotation frequency constant on cylinders r sin θ = const, vertical gravity becomes stronger with height on spheres of constant radius. On the other hand, effects of radial flux advection increase the flux density in the inner parts of the disc and lower the Eddington limit. In general, the effects connected to disc thickness tend to increase the local Eddington limit even more. The efficiency of accretion is however decreased by advection effects by about a factor of several.

Evidence for an expanding corona based on spectral-timing modelling of multiple black hole X-ray binaries

“…It is also possible that with the accretion rate increasing towards the Eddington limit, under the increasing radiation pressure, the disc becomes thicker again (e.g. Abramowicz et al 1988;Abolmasov & Chashkina 2015;Lančová et al 2019), resulting again in a strongly collimated jet.…”

The ergoregion in the Kerr spacetime: properties of the equatorial circular motion

“…For further consideration of a possible destruction of the horizon and naked singularity formation see, for example, [6,[51][52][53][54][55]. It is therefore possible that, during the evolutionary phases of the rotating object, the interaction with orbiting matter could lead to evolutionary stages of spin adjustment, in particular for example in the proximity of the extreme Kerr solution (with a M) where the speculated spin-down of the BH can occur preventing the formation of a naked singularity with a M (see also [5,7,10,44,[56][57][58][59][60][61] and [65]). On the other hand, the accreting matter can even get out, giving rise, for example, to Jets of matter or radiation [1].…”

“…Interacting with the surrounding matter and fields, an attractor can pass, during its evolution, through stages of adjustment of its spin, spin-down or spin-up processes see also [5,7,10,44,[56][57][58][59][60][61]. These phenomena will involve also the interaction of the accretor with matter and fields in the ergoregion (see, for example, [1]).…”

Modelling the spectral energy distribution of super-Eddington quasars

“…radial pressure terms become important, and H → R so rotation is sub-Keplarian. Radial advection of heat becomes important, so not all the energy released is radiated locally, and the inner edge of the flow is not necessarily set by R isco (Abramowicz et al 1988;Watarai et al 2000;Heinzeller & Duschl 2007;Abolmasov & Chashkina 2015). Nontheless, we can get use the thin disc equations to gain some physical insight into the results of more detailed numerical studies (see also Abramowicz 2005 for an insightful review).…”